Use of thermal insulation in apparel is well known, with conventional materials consisting of batting, foam, down and the like. By way of example, insulation for footwear is known to include leather, felt, fleece, cork, flannel, foam and combinations thereof. A disadvantage of conventional insulating materials is that the achievement of high levels of insulation requires the use of a relatively large thickness of material. For example, adequate insulation in footwear for sub-freezing temperatures is several centimeters thick. In many applications, the provision of a large thickness of material is impractical especially in apparel items for work or sport. In these activities, there often exists requirements of dexterity in the hands, surefootedness and firm traction for the feet, firm control of skis, skates or snowboards, or a reasonably close and firm fit for helmets. Too great a thickness of insulation introduces the possibility of relative motion between the body and the item being worn and hence an insecure contact with the ground or objects that must be handled. The esthetics of an article may also be affected by added thickness and users may be averse to wearing bulky items of apparel which have an unflattering or unfashionable appearance.
U.S. Pat. No. 4,055,699, to Hsiung teaches a multi-layer insole for an article of footwear to insulate the foot from cold which is sufficiently thin to insulate without changing fit. The insole is a multi-layered laminate having a thin soft fabric layer laminated to the top of an open cell foam layer, a dense cross-linked polyolefin layer laminated to the foam layer, and an aluminum coated barrier layer of polymeric material laminated to the bottom of the cross-linked polyolefin layer. It is taught, however, that the insole is compressible and the open celled layer tends to pump air as body pressure is alternately applied, circulating warm air around the side of the foot within the shoe. Additionally, to increase insulation it is taught to increasing the thickness of the open-celled layer.
U.S. Pat. No. 4,535,016, to Bradley teaches an insulating material for articles such as jackets, trousers sleeping bags, and the like. The insulation material includes a sealed envelope that is permeable to gas and which is made of a tightly woven or knitted material. The envelope is filled with a fine fibrous insulating material such as goose down, and between 3% to 50% by weight of a finely divided hydrophobic particulate metal or metalloid oxide pigment in an amount in excess of that required to cover all surfaces of the insulating material. The pigment material is added to increase insulating power and water repellency when compared to uncoated fibrous insulating material.
The thermal conductivity of conventional insulation material for apparel is generally greater than that of air which has a thermal conductivity of about 25 mW/m K at 25° C. In the case of high density materials such as neoprene foam, high conductivity may result from conduction by the solid component, or in materials of intermediate density a combination of both mechanisms may result in higher conductivity. Conventionally, to substantially increase the level of insulation, a substantial increase in insulation material is added, which has the above-stated disadvantages such as changing the fit of an article.
Insulation materials having lower thermal conductivities are known for use in the building sector, storage and transport equipment such as refrigerated transporters and trucks, appliances such as high temperature ovens and furnaces, containers for storage of liquids and gases, and the like. For example, powder-in-vacuum insulation is known, where panels of particulate material are contained in an impermeable cover or film under an internal pressure below atmospheric pressure.
U.S. Pat. No. 5,877,100, to Smith et al. teaches compositions with low thermal conductivity for use in insulation panels. The composite is a particulate composition which under 15 psi load at 20° C. and at a pressure within the range of 133.3-13332.2 Pa in nitrogen, has a packing density of less than or equal to 160 kg/m3, and a thermal conductivity of 4 to 6 mW/m K.
U.S. Pat. No. 4,159,359, to Pelloux-Gervais et al. teaches insulating materials used in buildings, refrigerators, ovens and furnaces. The insulating material is formed of a compacted structure having a low thermal conductivity. The compacted structure is formed of a fine silica-based, 100 angstrom particles, obtained by the heat treatment of a silane compound, which is compacted mechanically. At atmospheric pressure, the compacted structure is reported to have about twice the insulating performance of organic foams.
European Patent Publication No. 0 032 176 B2 to Degussa A G, teaches heat insulation mixtures that exhibit the least possible shrinkage at temperatures above 950° C. to minimize loss of heat-insulating properties. Insulation mixtures are compressed into boards, surrounded by porous enclosures and used for heat insulation of heat storage furnaces, decks and heating hoods. The heat insulation mixtures comprise pyrogenic silica, opacifier, inorganic fiber, and organosilicon compounds. While some low thermal conductivity insulation materials have enhanced insulation values, the utility of these materials is limited. Typically configured as large blocks or panels suitable for the above mentioned uses, the structures are thick and lack pliability.
Japanese Unexamined Patent Application No. 2-38385 teaches pliable insulating materials that may be used in non-planar arrangements, having low thermal conductivity. The insulating material comprises a pliable base material with open cells filled with fine particulate. The pliability of the open-celled material is taught to be unaffected by the fine particulate material which is formed by an anti-agglomeration treatment to ensure small void size within the cells. To avoid spillage of the particulate, the open-celled material may be covered with porous paper or air permeable film. It is taught that hermetic sealing of the insulating material would adversely affect pliability, and cause damage to the insulating material due to expansion of internal air from increase in temperature.
There is a need for articles of apparel having insulating components that provide greater insulation than conventional insulating materials, and which can be incorporated into apparel without substantially changing fit or appearance. Advantageously, such insulating components would be incompressible, having a lower thermal conductivity than conventionally used materials, and remain sufficiently pliable to meet the requirements of various apparel applications. The present invention is, therefore, directed to articles of apparel having insulating components which have substantially incompressible insulating structures and which have lower thermal conductivity than that of conventional insulating materials. The articles of apparel have pliable, flexible insulating structures that provide enhanced insulation without the addition of thick layers of insulating materials which disadvantageously affect the fit or functionality of the design of the article.